The present invention relates to an inkjet head printing device having an inkjet head for ejecting ink to a sheet of paper.
One of various types of conventional inkjet heads employed in the inkjet head printing device such as an inkjet printer is configured to have a fluid channel unit and an actuator unit. The fluid channel unit has a plurality of pressure chambers and a plurality of nozzles provided respectively for the plurality of pressure chambers. Ink introduced into the pressure chambers are ejected from the nozzles to form an image on the sheet of paper by selectively applying pressure to the pressure chambers using the actuator unit.
The actuator unit has a laminated structure consisting of a plurality of piezoelectric sheets and a common electrode layer. Further, a plurality of small electrodes are formed on one of the piezoelectric sheets for the plurality of the pressure chambers. The common electrode layer is maintained at a ground level. One of the piezoelectric sheets sandwiched between the common electrode layer, and the plurality of small electrodes is used as an active layer that is distorted when a voltage is applied thereto to apply presser to the pressure chambers.
The piezoelectric sheet has been polarized in a direction of its thickness. If a voltage is applied between the small electrode and the common electrode, the voltage is applied to a portion of the piezoelectric sheet (i.e., the active layer) in a direction of polarization of the piezoelectric sheet. Therefore, the portion of the piezoelectric sheet expands/contracts in the direction of its thickness by a vertical piezoelectric effect, which applies pressure to the pressure chamber to eject the ink from the nozzle.
It is desired to arrange the nozzles on the inkjet head more densely to increase resolution of images and/or to improve printing speeds. However, if the density of the nozzle is increased, i.e., the density of the pressure chambers is increased, a problem, that the amount of ejection of ink improperly increases or decreases relative to an appropriate of amount of ejection of the ink, or pressure chambers surrounding a target pressure chamber which is being applied with pressure are distorted by neighboring electrodes, occurs. Such a problem is frequently called a structural crosstalk. If the structural crosstalk occurs, quality of the image is deteriorated.
Japanese Patent Provisional Publication No. HEI 11-157076 discloses an inkjet head having a configuration for suppressing an effect of the structural crosstalk. According to the inkjet head disclosed in this publication, when a voltage is applied to a portion of a piezoelectric sheet corresponding to a target pressure chamber, which is targeted for application of pressure, a certain level of pressure which does not cause the nozzle to eject ink is also applied to neighboring pressure chambers surrounding the target pressure chamber.
According to the above mentioned configuration of the inkjet head disclosed in the publication, all of the pressure chambers are uniformly affected by their neighboring pressure chambers. Such configuration of the inkjet head enables to uniform the effects, caused by the structural crosstalk, on all of the nozzles of the inkjet head. Consequently, the amounts of the ink ejected from the nozzles become uniform, and thereby deterioration of the image is prevented.
However, in the publication, there is no explanation on how to control the inkjet head to represent gray scale on the image while suppressing the effect of the structural crosstalk.